This invention relates to a variable fill fluid coupling, and more specifically, it pertains to an improvement in the means for achieving filling of such a coupling with charging liquid.
Variable fill-type fluid couplings are used for coupling a variable-speed driver to a constant-speed output, or more commonly, to couple a constant-speed driver to an output device that requires a variable speed. For example, such couplings are particularly useful for driving centrifugal pumps that serve as booster pumps for water systems serving apartment houses and other buildings, wherein constant system pressures under varying flow conditions are desirable. Other applications can be found in municipal water systems and in commercial industrial processes.
Such variable-speed couplings are described in U.S. Pat. Nos. 3,210,940, 3,237,408, and 3,862,541 which are incorporated herein by this reference. Fluid couplings can be of the dual or double runner and impeller type, such as described in U.S. Pat. No. 3,210,940, or of the single runner and impeller type such as described in U.S. Pat. No. 3,862,541.
In both types of fluid couplings, liquid constantly bleeds from an active liquid working chamber in the coupling and charging liquid is constantly added thereto. A driving impeller and a driven runner are rotatably mounted in the working chamber and are coupled for joint rotation by the active liquid. The rate of bleeding of liquid from the active liquid chamber is established at a constant rate, while the rate of adding liquid thereto can be varied to change and to stabilize the volume of liquid in the chamber to provide a predetermined speed for the driven element of the coupling, under a given load.
In the aforementioned U.S. Pat. No. 3,210,940, a variable fill fluid coupling is disclosed where the active liquid working chamber of the coupling is charged by a positive displacement pump which is driven at a constant speed from the impeller shaft. The pump supplies the charging liquid from a sump at the bottom of the housing that encompasses the coupling. The active liquid chamber has a mouth for receiving charging liquid. The charging mouth is aligned with the longitudinal axis of the coupling, which is horizontally oriented. A charging chute directs the stream of charging liquid into the mouth. A charging stream splitter assembly is provided to determine the proportion of the charging liquid which enters the working chamber of the coupling with the balance of the charging liquid being bypassed and returned to the sump. The more charging liquid introduced into the working chamber, the faster the driven runner rotates.
U.S. Pat. No. 3,862,541 shows a modification of the coupling shown in U.S. Pat. No. 3,210,940. The modification includes the use of a nozzle for directing charging liquid to the mouth of the fluid coupling. An advantage of the use of the nozzle is a faster response between a change in the control setting of the fluid coupling and the resultant change of speed of the driven runner.
In at least two instances, there is difficulty in insuring that all of the charging liquid directed at the mouth of the fluid coupling actually enters the active liquid chamber. One such problem exists when the mouth faces downwardly so that charging liquid needs to be forced upwardly into the mouth. Due to the force of gravity acting on the charging liquid, a portion of the charging liquid that is supposed to pass through the mouth into the working chamber actually flows downwardly into the liquid sump.
Another problem can occur with large fluid couplings. For large fluid couplings, a support member is placed within the mouth to provide structural support. The support member, although it has openings for charging liquid, restricts flow of charging liquid through the mouth. At high rates of flow of the charging fluid, a condition that is required when rapid increases and high output speeds are required, charging liquid can splash back off the support member and into the sump. This problem is of course compounded when a large fluid coupling having a support member in the mouth is oriented so that the charging liquid is introduced upwardly into the mouth against the force of gravity.
The result of these problems is that the liquid volume in the working liquid chamber cannot be increased rapidly in response to external signals to the control mechanism which may require timely and rapid output speed increases. This results in the device connected to the output shaft of the fluid coupling rotating at a speed lower than desired for a longer period of time than acceptable, with an unacceptable resultant loss in magnitude of the output speed.
In view of these problems, it is apparent that there is need for a variable fill fluid coupling which, even when the mouth is facing downwardly and/or the mouth has an obstruction, is able to take in large amounts of charging liquid rapidly when required to do so.